Food poisoning, also called foodborne illness, is illness caused by eating contaminated food. Infectious organisms — including bacteria, viruses and parasites — or their toxins are the most common causes of food poisoning.

Infectious organisms or their toxins can contaminate food at any point of processing or production. Contamination can also occur at home if food is incorrectly handled or cooked.

Food poisoning symptoms, which can start within hours of eating contaminated food, often include nausea, vomiting or diarrhea. Most often, food poisoning is mild and resolves without treatment. But some people need to go to the hospital.

Food poisoning symptoms vary with the source of contamination. Most types of food poisoning cause one or more of the following signs and symptoms:

Nausea

Vomiting

Watery diarrhea

Abdominal pain and cramps

Fever

Signs and symptoms may start within hours after eating the contaminated food, or they may begin days or even weeks later. Sickness caused by food poisoning generally lasts from a few hours to several days.

When to see a doctor

If you experience any of the following signs or symptoms, seek medical attention.

Neurological symptoms such as blurry vision, muscle weakness and tingling in the arms

Contamination of food can happen at any point during its production: growing, harvesting, processing, storing, shipping or preparing. Cross-contamination — the transfer of harmful organisms from one surface to another — is often the cause. This is especially troublesome for raw, ready-to-eat foods, such as salads or other produce. Because these foods aren't cooked, harmful organisms aren't destroyed before eating and can cause food poisoning.

Many bacterial, viral or parasitic agents cause food poisoning. The following table shows some of the possible contaminants, when you might start to feel symptoms and common ways the organism is spread.

Seafood and raw, ready-to-eat produce. Can be spread by an infected food handler.

Staphylococcus aureus

1 to 6 hours

Meats and prepared salads, cream sauces, and cream-filled pastries. Can be spread by hand contact, coughing and sneezing.

Vibrio vulnificus

1 to 7 days

Raw oysters and raw or undercooked mussels, clams, and whole scallops. Can be spread through contaminated seawater.

Whether you become ill after eating contaminated food depends on the organism, the amount of exposure, your age and your health. High-risk groups include:

Older adults. As you get older, your immune system may not respond as quickly and as effectively to infectious organisms as when you were younger.

Pregnant women. During pregnancy, changes in metabolism and circulation may increase the risk of food poisoning. Your reaction may be more severe during pregnancy. Rarely, your baby may get sick, too.

Infants and young children. Their immune systems haven't fully developed.

People with chronic disease. Having a chronic condition — such as diabetes, liver disease or AIDS — or receiving chemotherapy or radiation therapy for cancer reduces your immune response.

The most common serious complication of food poisoning is dehydration — a severe loss of water and essential salts and minerals. If you're a healthy adult and drink enough to replace fluids you lose from vomiting and diarrhea, dehydration shouldn't be a problem.

Infants, older adults and people with suppressed immune systems or chronic illnesses may become severely dehydrated when they lose more fluids than they can replace. In that case, they may need to be hospitalized and receive intravenous fluids. In extreme cases, dehydration can be fatal.

Some types of food poisoning have potentially serious complications for certain people. These include:

Listeria monocytogenes. Complications of a listeria food poisoning may be most severe for an unborn baby. Early in pregnancy, a listeria infection may lead to miscarriage. Later in pregnancy, a listeria infection may lead to stillbirth, premature birth or a potentially fatal infection in the baby after birth — even if the mother was only mildly ill. Infants who survive a listeria infection may experience long-term neurological damage and delayed development.

Escherichia coli (E. coli). Certain E. coli strains can cause a serious complication called hemolytic uremic syndrome. This syndrome damages the lining of the tiny blood vessels in the kidneys, sometimes leading to kidney failure. Older adults, children younger than 5 and people with weakened immune systems have a higher risk of developing this complication. If you're in one of these risk categories, see your doctor at the first sign of profuse or bloody diarrhea.

If you or your child needs to see a doctor, you'll likely see your primary care provider first. If there are questions about the diagnosis, your doctor may refer you to an infectious disease specialist.

What you can do

Preparing a list of questions will help you make the most of your time with your doctor. Some questions to ask include:

What's the likely cause of the symptoms? Are there other possible causes?

Is there a need for tests?

What's the best treatment approach? Are there alternatives?

Is there a need for medication? If yes, is there a generic alternative to the medicine you're prescribing?

How can I ease the symptoms?

What to expect from your doctor

Some questions the doctor may ask include:

Has anyone in your family or otherwise close to you developed similar symptoms? If so, did you eat the same things?

Have you traveled anywhere where the water or food might not be safe?

Are you having bloody bowel movements?

Do you have a fever?

Had you taken antibiotics in the days or weeks before your symptoms started?

When did symptoms begin?

Have the symptoms been continuous, or do they come and go?

What foods have you eaten in the past few days?

What you can do in the meantime

Drink plenty of fluids. Stick with bland foods to reduce stress on your digestive system. If your child is sick, follow the same approach — offer plenty of fluids and bland food. If you're breast-feeding or using formula, continue to feed your child as usual.

Food poisoning is often diagnosed based on a detailed history, including how long you've been sick, your symptoms and specific foods you've eaten. Your doctor will also perform a physical exam, looking for signs of dehydration.

Depending on your symptoms and health history, your doctor may conduct diagnostic tests, such as a blood test, stool culture or examination for parasites, to identify the cause and confirm the diagnosis.

For a stool culture, your doctor will send a sample of your stool to a laboratory, where a technician will try to identify the infectious organism. If an organism is found, your doctor likely will notify your local health department to determine if the food poisoning is linked to an outbreak.

In some cases, the cause of food poisoning can't be identified.

Treatment for food poisoning typically depends on the source of the illness, if known, and the severity of your symptoms. For most people, the illness resolves without treatment within a few days, though some types of food poisoning may last longer.

Treatment of food poisoning may include:

Replacement of lost fluids. Fluids and electrolytes — minerals such as sodium, potassium and calcium that maintain the balance of fluids in your body — lost to persistent diarrhea need to be replaced. Some children and adults with persistent diarrhea or vomiting may need hospitalization, where they can receive salts and fluids through a vein (intravenously), to prevent or treat dehydration.

Antibiotics. Your doctor may prescribe antibiotics if you have certain kinds of bacterial food poisoning and your symptoms are severe. Food poisoning caused by listeria needs to be treated with intravenous antibiotics during hospitalization. The sooner treatment begins, the better. During pregnancy, prompt antibiotic treatment may help keep the infection from affecting the baby.

Adults with diarrhea that isn't bloody and who have no fever may get relief from taking the medication loperamide (Imodium A-D) or bismuth subsalicylate (Pepto-Bismol). Ask your doctor about these options.

Food poisoning often improves without treatment within 48 hours. To help keep yourself more comfortable and prevent dehydration while you recover, try the following:

Let your stomach settle. Stop eating and drinking for a few hours.

Try sucking on ice chips or taking small sips of water. You might also try drinking clear soda, clear broth or noncaffeinated sports drinks, such as Gatorade. You're getting enough fluid when you're urinating normally and your urine is clear and not dark.

Wash your hands, utensils and food surfaces often. Wash your hands well with warm, soapy water before and after handling or preparing food. Use hot, soapy water to wash utensils, cutting boards and other surfaces you use.

Cook foods to a safe temperature. The best way to tell if foods are cooked to a safe temperature is to use a food thermometer. You can kill harmful organisms in most foods by cooking them to the right temperature.

Refrigerate or freeze perishable foods promptly — within two hours of purchasing or preparing them. If the room temperature is above 90 F (32.2 C), refrigerate perishable foods within one hour.

Defrost food safely. Don't thaw food at room temperature. The safest way to thaw food is to defrost it in the refrigerator. If you microwave frozen food using the "defrost" or "50 percent power" setting, be sure to cook it immediately.

Throw it out when in doubt. If you aren't sure if a food has been prepared, served or stored safely, discard it. Food left at room temperature too long may contain bacteria or toxins that can't be destroyed by cooking. Don't taste food that you're unsure about — just throw it out. Even if it looks and smells fine, it may not be safe to eat.

Food poisoning is especially serious and potentially life-threatening for young children, pregnant women and their fetuses, older adults, and people with weakened immune systems. These individuals should take extra precautions by avoiding the following foods:

Raw or rare meat and poultry

Raw or undercooked fish or shellfish, including oysters, clams, mussels and scallops

Raw or undercooked eggs or foods that may contain them, such as cookie dough and homemade ice cream

Raw sprouts, such as alfalfa, bean, clover and radish sprouts

Unpasteurized juices and ciders

Unpasteurized milk and milk products

Soft cheeses, such as feta, Brie and Camembert; blue-veined cheese; and unpasteurized cheese

Refrigerated pates and meat spreads

Uncooked hot dogs, luncheon meats and deli meats

References

Centers for Disease Control and Prevention, et al. Diagnosis and management of foodborne illnesses: A primer for physicians and other health care professionals. MMWR. 2004;53:1. http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5304a1.htm. Accessed April 16, 2014.

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